Isolators are used in the field of vibration management. Vibration isolators try to isolate a vibration sensitive device (payload) from a vibratory disturbance (base motion). Typically vibration isolators are designed to be soft (low in natural frequency) so that base motion may be accommodated (absorbed) while reducing a force transmitted to the payload. Frequently it becomes difficult to lower an isolator's natural frequency to provide sufficient isolation at certain frequencies where excitations may be concentrated. For example, narrow-band vibration disturbances may occur in situations such as, spin rates of reaction wheels, control moment gyros on space craft, compressor drive speeds in refrigeration and cryocooler systems, and turbine and engine speeds.
Lowering an isolator's natural frequency is typically accomplished by softening a compliant element of an isolator. In lieu of softening the compliance, mass may be added to the payload to assist in lowering the natural frequency. Simply softening an isolator can make it sag due to gravity, leading to loss of clearance or high stresses in the flexural elements. Too much mass, either in the payload or the isolator, is undesirable in situations where light weight is required, especially in spacecraft and airplanes.